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Pmt111500

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THC origins in the Antarctic side faltering?
« on: April 12, 2013, 07:22:53 AM »
FishOutofWater attempts to connect various recent articles on Antarctic Sea Ice, ice sheet meltdown, and changes of global scale THC (ThermoHaline Circulation) into a coherent piece and does pretty well in my opinion, but as dailykos is an opinion site , there maybe some glitches (am I correct with the word? glitch - minor error,  logical jump jumping over some fact , or similar) in it. Usually FOoW's diaries are pretty well researched, but on this occasion I do not know if this is the case. 

http://www.dailykos.com/story/2013/04/10/1200602/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-Is-Faltering
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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #1 on: April 14, 2013, 04:13:55 AM »
In my opinion FishOutofWater's post is generally well researched and I agree with most of his/her information; however, I am concerned that some of his/her language may lead some readers to be concerned that the thermohaline circulation (THC) is going to stop; for example FishOutofWater makes the following statement:
"Update from the comments
I have been asked what's going to happen in response to the faltering of the thermohaline circulation around Antarctica. This post is based on a synthesis of very recent research reports. The key report, that found the layer of fresh water between 50 and 150 meters deep, was just published. Deward Hastings explained, in a comment, how disruptive this lens of freshened water could be to the earth's climate system and our models of it:


it IS complicated, and confusing
That lens of (relatively) fresh water that is forming around Antarctica is challenging, and changing, almost everything in global circulation patterns.  It freezes sooner (and at a higher temperature).  That shields the water from the wind, and reduces wind-driven mixing.  It reduces, perhaps to the point of stopping altogether, the present global ocean circulation patterns.  That in turn will change global atmospheric weather.

Nobody knows exactly what comes next.  We've never seen it happen, and our models, not terribly accurate in describing the world we know, are completely untested in the coming world that we don't know."

In this regard, I would prefer to use the word "slowing" instead of "faltering" as I do not believe that the THC will "stop" now, or in the future.  Thus, while I agree that the reduction in AABW production will slow the THC (which will induce numerous and complex changes worldwide); I believe these changes will be much slower to unfold than will the impacts of the increasingly warm CDW on the Antarctic ice sheets (most significantly on the WAIS).
« Last Edit: April 14, 2013, 02:22:30 PM by AbruptSLR »
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Donna

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Re: THC origins in the Antarctic side faltering?
« Reply #2 on: April 14, 2013, 05:36:44 AM »
Quote
In this regard, I would prefer to use the word "slowing" instead of "faltering" as I do not believe that the THC will "stop" now, or in the future.  Thus, while I agree that the reduction in AABW production will slow the THC (which will induce numerous and complex changes worldwide); I believe these changes will be much slower to unfold than will the impacts of the increasingly warm CDW on the Antarctic ice sheets (most significantly on the WAIS).
 

Many thanks AbruptSLR, your opinion is greatly appreciated. 

Donna

Pmt111500

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Re: THC origins in the Antarctic side faltering?
« Reply #3 on: April 14, 2013, 05:50:03 AM »
Thanks for the review, AbruptSLR, appreciated. The physics and movements of water and ice masses round Antarctica are complicated and it's nice to hear that there's only a little dose (faltering - slowing) of exaggeration at DailyKos in this.
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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #4 on: April 14, 2013, 02:36:07 PM »
Pmt111500/Donna,

The following abstract indicates that possible future increases in Antarctic circumpolar wind speed could possibly help to restore the production of AABW in the future.


On challenges in predicting bottom water transport in the Southern Ocean
Oleg A. Saenko, Alex Sen Gupta and Paul Spence
Corresponding author; E-mail: Oleg.Saenko@ec.gc.ca
Journal of Climate
July 27, 2011

"ABSTRACT
Changes in the Southern Ocean lower-limb overturning circulation are analyzed using a set
of climate models. In agreement with some recently developed theoretical models, it is found
that the overturning can be strongly affected by winds. In particular, the simulated strengthening
of large-scale southward transport in the abyss is explicitly driven by zonal wind stress.
However, there is a considerable range among the climate models in their projected changes of
Southern Ocean wind stress. Furthermore, the strengthening of large-scale southward transport
tends to be compensated by eddy-induced northward flows in the abyss, particularly at eddypermitting resolution. As a result, the net Antarctic Bottom Water export may only be weakly
affected. However, none of the models considered accounts for the possibility that a fraction
of the eddy kinetic energy may be converted to diapycnal mixing. If this were the case, the
presented energetic arguments suggest that stronger Southern Ocean winds would result in a
stronger AABW transport."
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Bruce Steele

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Re: THC origins in the Antarctic side faltering?
« Reply #5 on: April 15, 2013, 07:04:05 PM »
  I didn't understand that geothermal heating was what caused warming and thermal expansion of the abyssal waters.  So as flow rates slow in Antarctic deep water formation geothermal heating would possibly? have more contact with a smaller volume of water? Here is a short summary written by Purkey last month.      The extra heating question is mine. About .03 degrees C temp. change per decade in deep waters of the southern hemisphere. A rate ten times that of heating for waters of the abyssal waters of the northern hemisphere.                                                            http://www.livescience.com/28248-deep-ocean-warming.html           

AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #6 on: April 16, 2013, 01:37:40 AM »
Bruce,

Thanks for the very interesting article.  I didn't know either that the abyssal water warms by geothermal heating (as well as mixing with the warmer water above) as it travels around the world.  It would seem that as the abyssal water warms it should absorb geothermal energy at a slower rate, but if the abyssal water is in contact with the seafloor for a longer period maybe it will expand more.

Best, ASLR
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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #7 on: April 16, 2013, 02:13:44 AM »
This links to a summary of how cloud cover over the Southern Ocean affect change of rain patterns in the tropics:

http://www.washington.edu/news/2013/03/11/remote-clouds-responsible-for-climate-models-glitch-in-tropical-rainfall/
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Bruce Steele

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Re: THC origins in the Antarctic side faltering?
« Reply #8 on: April 16, 2013, 02:56:18 AM »
Super cold wind blowing across a polynya, ice formation and saline ejection , all the reasons that explain deep water formation seem logical.  The processes that eventually bring that cold salty water back to the surface waters( less than 500 meters ) aren't as apparent , well not to me anyhow. As the deep( or intermediate ) water sinks it ventilates the deep waters with oxygen, surface Co2 , and organic matter .   When that water has spent long periods away from the surface the O2 drops and the Co2 increases as the organic matter is remineralized.  If the Antarctic Deep Water continues to decline it will undoubtably change the amount of time it takes these deep currents to transit the globe. How that will change the way those deep waters eventually resurface I haven't a clue.   
« Last Edit: April 16, 2013, 04:29:39 AM by Bruce Steele »

Bruce Steele

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Re: THC origins in the Antarctic side faltering?
« Reply #9 on: April 16, 2013, 07:22:01 AM »
" Geothermal heat flux is systematically positive, thus supplying buoyancy to bottom water. Geothermal heating tends to transform the densest water masses into warmer, lighter water,much like air-sea fluxes transform surface waters."      From the paper below                                                    http://www.ocean-sci-discuss.net/5/281/2008/osd-5-281-2008.pdf

 
« Last Edit: April 16, 2013, 07:38:30 AM by Bruce Steele »

AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #10 on: April 23, 2013, 12:49:29 AM »
The first attached figure show a map of global distribution of salinity differences in ocean water around the world primarily resulting from differences of precipitation and evaporation in the different indicated areas.  The second attached figure shows a map of the distribution of salinity differences in the Southern Ocean water; which in addition to precipitation and evaporation is largely influenced by ice meltwater from the Antarctic ice shelves and ice sheets; which in turn in contributing to the current increase in Antarctic sea ice area and to a reduction in the production of Antarctic Bottom Water, AABW.
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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #11 on: June 21, 2013, 10:26:13 PM »
For those more interested in the AABW trends than the CDW trends, I provide the following two images from the following paper, which quantify the trend of decreasing AABW temperature from the Weddell Sea area.
Synchronous intensification and warming of Antarctic Bottom Water outflow from the Weddell Gyre
By: Michael P. Meredith, Arnold L. Gordon, Alberto C. Naveira Garabato, E. Povl Abrahamsen, Bruce A. Huber, Loïc Jullion, and Hugh J. Venables
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L03603, doi:10.1029/2010GL046265, 2011.
The caption for the first image is labeled Figure 1, below and the caption for the second image is labeled Figure 2, below:
Figure 1. Locations of M2 and MYRTLE in the northern Weddell Sea and southern Scotia Sea (red dots). Yellow arrows depict the primary flow paths of WSDW through the region: Orkney Passage (OP) on the South Scotia Ridge and Georgia Passage (GP) at the northeastern Scotia Sea are key throughflows. The Southern Boundary (SB) of the Antarctic Circumpolar Current is marked. Background shading is depth (m). Inset shows typical potential temperature and buoyancy frequency profiles from the location of M² (red) and close to the site of MYRTLE (black). The depths of the MYRTLE and M2 temperature sensors used here are marked.

Figure 2. (a–e) Temperature anomaly at M2 (black) and MYRTLE (red), for lags of 0 to 120 days. MYRTLE and
M2 correlate well at 120 days lag, except for the first ∼9 months, during which a 60 day lag yields the highest correlation (shaded boxes in Figures 2a and 2c highlight these periods). (f) Zonal wind stress averaged over the northern Weddell Sea (area of averaging marked in Figure 3a). Curve is a five‐point running average of monthly‐mean values, plotted inverted. Shaded box is as per Figure 2c, during which period wind forcing reached a record‐length extreme. (g) As for Figure 2f, but for the full length of ERA‐Interim.
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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #12 on: June 27, 2013, 08:31:40 PM »



The Australians are currently studying Mertz Glacier's (see attached figure) contribution to the AABW that feeds into the Indian Ocean.  The following is an old internet summary describing those on-going efforts:

"The Mertz Glacier's in a region of Antarctica known as one of the three lungs of the oceanBy Emma Jolliff
Reporter
The Tangaroa, which famously released Wellington's resident penguin, Happy Feet, is returning to Antarctica.
This time scientists are going to study waters around the Mertz Glacier, part of which broke off two years ago, to see if melting Antarctic ice is changing the ocean.
The Mertz Glacier's in a region of Antarctica known as one of the three lungs of the ocean. The other two are in the Ross Sea and the Weddell Sea in the southern Atlantic Ocean.
“Literally it's somewhere oxygen gets into the deep ocean,” says oceanographer Mike Williams.
It also includes as carbon dioxide from the atmosphere.
Now scientists fear that “lung” has shut down.
Oceanographer Mr Williams is leading a 42-day mission to test the theory that increased melting of Antarctic ice is driving changes in the deep ocean.
Mr Williams says the region was dependent on the Mertz Glacier tongue, which was rammed by an iceberg three years ago and broke away.
It's been pushed it out to sea, blocking local ocean currents and changing the distribution of ice. What that means for the region is unclear.
The polar regions have been acting as the Earth's canaries in a coal mine.
“If our canary's not working that's quite important for us because all of a sudden it might start screaming things have changed,” he says.
Twenty-two scientists will be working in the Mertz Polynya, an area of open water surrounded by sea ice the size of Lake Taupo. Two years ago Australian scientists left scientific instruments among the ice flows.
“We'll be using instruments on the Tangaroa to go all the way down to the bottom and profile how salty is the ocean, how cold it is, to see how things have changed from other years.”
The $3.5-million mission has been in the planning for four years. The Tangaroa leaves Wellington this evening."


Read more: http://www.3news.co.nz/Melting-glaciers-may-affect-ocean-oxygen-levels/tabid/1160/articleID/285374/Default.aspx#ixzz2MX1cu5Us

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AbruptSLR

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Re: THC origins in the Antarctic side faltering?
« Reply #13 on: July 25, 2013, 11:54:50 PM »
While I already posted this reference in the "Southern Ocean" thread; it is so important to the THC (and its possible faltering) that I am reposting both the reference and the Wikipedia link below explaining the AAIW:

http://en.wikipedia.org/wiki/Antarctic_Intermediate_Water

Non-linear climate responses to changes in Antarctic Intermediate Water
by: Jennifer A. Graham;  David P. Stevens & Karen J. Heywood; Journal of Climate 2013; doi: http://dx.doi.org/10.1175/JCLI-D-12-00767.1 

Abstract
"The global impact of changes in Antarctic Intermediate Water (AAIW) properties is demonstrated using idealized perturbation experiments in a coupled climate model. Properties of AAIW were altered between 10 and 20°S in the Atlantic, Pacific and Indian oceans separately. Potential temperature was changed by ±1°C, along with density-compensating changes in salinity. For each of the experiments, sea surface temperature responds to changes in AAIW, when anomalies surface at higher latitudes (> 30°). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean, resulting in non-linear responses to opposite sign perturbations. In the Southern Ocean, these affect the meridional density gradient, leading to changes in Antarctic Circumpolar Current transport. The response to cooler, fresher AAIW is both greater in magnitude and significant over a larger area than that for warmer, saltier AAIW. The North Atlantic is particularly sensitive to cool, fresh perturbations, with density anomalies causing reductions in the meridional overturning circulation of up to 1 Sv. Resultant changes in meridional ocean heat transport, along with surfacing anomalies, cause basin-wide changes in the surface ocean and overlying atmosphere on multi-decadal time-scales."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson